Grease manufacturers have attempted to prepare biodegradable alkali and alkaline earth metal greases from vegetable oils with limited success. The high temperatures required degrades the vegetable oil thickener substrate and vegetable oil diluent. The only success is in using mineral oil during the formation of the thickener, then adding vegetable oil as a diluent.
U.S. Pat. No. 3,242,088 (Bright et al., Mar. 22, 1966) provides a low temperature method for the preparation of soap thickened greases, wherein increased yields and improved product quality are obtained. The method of this reference involves essentially carrying out the saponification step of the grease making process by slowly introducing a solution or slurry of metal base into a recirculating stream of lubricating oil and saponifiable material at an elevated temperature sufficient to produce a rapid reaction between the metal base and the saponifiable material and thereafter subjecting the recirculated stream to turbulent mixing before returning it to the main body of saponification mixture. Very advantageously, the stream may be subjected to shearing, most suitably by passing it through a shear valve with at least a substantial pressure drop across the valve. The process representing the preferred embodiment of this reference comprises recirculating the grease mixture in the same manner during the subsequent heating at higher temperatures, with shearing by means of a shear valve during at least a portion of the further heating step.
U.S. Pat. No. 4,392,967 (Alexander, Jul. 12, 1983) provides a process for continuously manufacturing a lubricating grease using a screw process unit comprising:
(a) introducing feed materials and lubricating oil into selected locations of a screw process unit which contains a series of adjacent, longitudinally connected barrel sections for performing different operative steps and houses a rotating screw device traversing the interior of the barrel sections and having separate elements along its length to perform desired operations;
(b) mixing and conveying said feed materials along said process unit through the adjacent barrel sections by continuous operation of said rotating screw;
(c) controlling the temperature of said material while it is being conveyed through said process unit by use of various heat exchange means which are located in or adjacent each barrel to said in carrying out the operative steps of dispersion, reaction, dehydration and/or homogenization;
(d) venting water resulting from the dehydration of the feed mixture at selected barrel discharge points in said process unit;
(e) introduction of additional lubricating oil and/or additives at downstream barrel locations following the dehydration step;
(f) homogenization of said complete grease formulation by continued rotation of said screw device; and
(g) removal of the finished lubricating grease from the end barrel section of said screw process unit.
U.S. Pat. No. 4,597,881 (Iseya et al., Jul. 1, 1986) provides a process for producing a lithium-soap grease which comprises:
adding a hydroxy-fatty acid having from 12 to 24 carbon atoms, and a dicarboxylic acid having from 8 to 10 carbon atoms to a base oil (I) having an aniline point of from 100.degree. to 130.degree. C. at a temperature of less than 100.degree. C. with stirring to prepare a uniform dispersion of said acids in the base oil (I);
adding lithium hydroxide to said uniform dispersion with stirring;
reacting said acids and lithium hydroxide and dehydrating by heating to a temperature of 195.degree. to 210.degree. C.;
cooling the reaction mixture to a temperature not higher than about 160.degree. C. at a cooling rate of from about 20.degree. to 80.degree. C./hour; and
adding a base oil (II) having an aniline point of from 130.degree. to 140.degree. C. to the reaction mixture for a period of from 10 seconds to 30 minutes in an amount so that the weight ratio of the base oil (I) to the base oil (II) is from 30:70 to 60:40 and the resulting mixture of the base oils (I) and (II) has a dynamic viscosity as determined at 100.degree. C. of from 5 to 50 centistokes and an aniline point of from 125.degree. to 135.degree. C. to produce said lithium-soap grease.
U.S. Pat. No. 4,902,435 (Waynick, Feb. 20, 1990) relates to a lubricating grease which is particularly useful for front-wheel drive joints. The grease displayed good results over prior art greases. The grease provides superior wear protection from sliding, rotational, and oscillatory (fretting) motions in front wheel drive joints. It is also chemically compatible with elastomers and seals in front-wheel drive joints. It further resists chemical corrosion, deformation, and degradation of the elastomers and extends the useful life of CV (constant velocity) drive joints.
U.S. Pat. No. 5,350,531 (Musilli, Sep. 27, 1994) provides a process for preparing a 12-hydroxy calcium lithium stearate grease. In the first step of the process, 12-hydroxy stearic acid is mixed with a first portion of a paraffin bright stock oil and thereafter heated to a temperature of from about 170 to about 200 degrees Fahrenheit. Thereafter, lithium hydroxide and calcium hydroxide are added to the mixture, the mixture is then heated to a temperature of from about 360 to about 450 degrees Fahrenheit and saponified, and then the product is comminuted. The comminuted mixture is then mixed with a second portion of lubricating oil.